The use of dispersants to disperse fillers and pigments in liquid media is state of the art and involves, in principle, using such additives to fullfill the following tasks:    (1) An easier incorporation of fillers and pigments, in order to ensure shorter dispersing times at plant level or to allow the utilization of simple dispersing equipment (dissolvers rather than beadmill dispersing),    (2) A reduction in the viscosity of pigment pastes or of inks and paints, absent which the production of very highly filled pigment pastes is completely impossible,    (3) The development of optimum color strength or of optimum hiding power in the case of opaque pigments,    (4) The prevention of the propensity of pigment pastes to undergo settling when stored for a number of months, in transit and under extreme climatic exposure,    (5) The prevention of flocculation in order to produce reproducible shades, which is particularly important as a result of the use of paint-mixing machines for coloring different kinds of white base paints and base varnishes, and    (6) The establishment of compatibility with a large number of letdown binders or, additionally, of paints and inks produced from them.
The fundamental tasks of a dispersant or of such auxiliaries, described above, should first be fed independently of the question of the particular liquid medium in which a filler or pigment is to be dispersed.
In the manner in which the desired effect is achieved, however, dispersants are frequently very variable. It is necessary to consider how independently a dispersant operates from the pigment used, in other words how universally it acts in respect of different kinds of pigment and filler surfaces (organic or inorganic, hydrophobically or hydrophilically modified, etc.).
This function can often still be met by modern-day polymeric dispersant structures. Descriptions are given, for example, of water-soluble polyisocyanate adducts containing hydrophilic polyether chains (EP-A-0 731 148), hydrophilic polyurethane-polyureas (DE-A-44 16 336), poly(meth)acrylates (U.S. Pat. No. 3,980,602, WO-A-94/21701), and also specialty polyesters (WO-A-94/18260) or copolymers based on vinylic monomers (styrene, vinylimidazole, etc.) with acrylate-functional monomers (acrylic cid, BuAc, HEA), as in EP-B-0 311 157.
Besides the disruptive or even toxic residues of monomer, however, these systems frequently lack universal compatibility with the typical binder systems.
Because of molar weight, the nature of the monomers used or the long polyethylene oxide chains that are needed for water solubility, the resulting products are frequently solid and can be formulated by neutralization generally only as 40% strength aqueous solutions, thereby restricting the user in the case where highly concentrated pastes are produced.
A far greater problem, however, is that of the universality of the dispersant for different kinds of surroundings.
The fundamental assumption is that in aqueous, hydrophilic media it is necessary to take account not only of the steric stabilization of the pigment by the dispersant, but also of an electrostatic contribution to stabilization, which, if functional groups are suitably chosen, is not available in this way for dispersing in a solvent-containing environment or in other hydrophobic media such as UV systems.
In the last-mentioned systems, the action of dispersants is primarily through steric stabilization. It is therefore understandable that dispersants must have a certain compatibility with the medium surrounding them in order for there to be the steric stabilization, through the maintenance of sufficient distance between the pigment particles. Those components of dispersants (side chains in polymers and/or block components in linear structures) which take on this stabilizing function are not capable of being able to be equally effective in a hydrophilic and a hydrophobic environment, owing to the stringent requirements imposed on the different kinds of pigments. This is essentially a question of the solubility and compatibility with the surrounding matrix.
It is therefore state of the art today that, owing to the diverse efforts, different kinds of dispersant structures have been developed on one hand for aqueous and water-thinnable paints and inks and, on the other hand, that there are dispersants for solvent-borne and UV-based systems, respectively. In other words, the scheme which has come about (see, FIG. 1 which is referred herein as scheme (1)) is a different kind of color paste system for coloring the aqueous and the solvent-borne systems, respectively, on the basis of the aforementioned dispersant groups.
In light of the associated logistical effort and microeconomic expense involved in producing and storing different kinds of pigment paste systems for paint-mixing machines, there is therefore a high potential for savings, which has already been acknowledged by certain developments in more recent times, through the use of what are called universal dispersants.
So-called universal dispersants are used for formulating aqueous pigment pastes and are formulated, for example, on the basis of alkylphenol ethoxylates (J. Bieleman, PPCJ 3, 1995, 17; P. Quednau, ACT'98, Paper No. 29), oleo-block-ABC derivatives (H. Frommelius, VILF (Verband der lngenieure für Lacke und Farben) Janrestagung [annual conference] 2000, 41) or styrene-oxide-based polyether structures (6th Nuremberg Congress, Creative Advances in Coatings Technology, April 2001, 481, Vincentz K G). Nevertheless the ecotoxicologically objectional alkylphenol ethoxylates (Journal of Surfactants and Detergents, Vol.5, No.1, (2002); Critical reviews in Toxicology, 26(3): 335-364, (1996); P. Schöberl, Tenside Surfactants Detergents 25, 1988, 2, 86; K. Fent, Swiss Federal Institute for Environmental Science and Technology) are as unsuccessful as the other concepts for universal dispersants for allowing the successful coloring of all existing systems.
When used alone in water-based universal pastes (which can contain up to 20% solvent in the form, for example, of a humectant), they are only capable of tinting aqueous paints and inks, based for example on acrylate dispersions, hybrid binders or PVAc terpolymers, and of coloring a narrowly restricted, selected assortment of solvent-based inks and paints, such as conventional alkyd resin paints or PU alkyd-based systems, for example.
So-called universal pastes are completely unsuitable, however, for coloring solvent-borne paints and inks based, for example, on Pliolite (styrene-acrylates or styrene-butadienes in solution, for example, in white spirit or isoparaffins) or Isopar-based alkyd resins or systems known as high-solids alkyds. Solvent-based pastes have been employed for this function to date.
In view of the fact that in conventional paint-mixing machines there are 12 to 20 color pastes with different pigments, the market's requirement not to have to install a plurality of paint-mixing machines, each containing pastes suitable only for coloring particular white paints and varnishes, becomes clearly understandable.